This invention relates to a non-contact displacement detecting device, particularly, this invention relates to a bushing mechanism of a rotational member.
Conventionally, a non-contact displacement detecting device (e.g., non-contact detecting sensor) includes a rotational shaft fixed with a detected object, the rotational shaft is fixed with a permanent magnet, and a Hall element (e.g., Hill IC) is disposed facing the permanent magnet with a predetermined clearance. When the detected object rotates, the permanent magnet fixed with the rotational shaft is rotated as well. As a result, a magnetic flux closing over the Hall element changes, and the sensor detects a movement of the rotational shaft by detecting a change of the magnetic flux.
For example, the non-contact displacement detecting device such as this is disclosed in Japanese Patent laid open No. Hei 02 (1990)-122205. The publication discloses a rotational shaft inserted into a housing made of resin with a bushing function. One end portion of the rotational shaft is fixed with the cross-sectional approximately U-shaped a magnet holder with the permanent magnet at a inner surface thereof. Movement in one axial direction of the rotational shaft is restricted by the boss portion at the center of the housing; with movement in another axial direction of the rotational shaft, a groove portion is formed on an outer surface of the rotational shaft so as to be restricted by an end portion of an opposite side of the boss portion in which the rotational shaft is inserted. The non-contact displacement detecting device includes a restricting mechanism restricted in the movement of the axial direction of the rotational shaft by fitting a clip in the groove portion.
However, when the movement in one axial direction is restricted by the boss portion of the housing and the magnet holder, the movement in another direction is restricted by the clip fitting at the groove portion of the rotational shaft. A groove proofing on the rotational shaft, and extra parts (e.g., a clip restricting the movement of the rotational shaft in the axial direction and a ring member etc) are needed. As a result, the cost of the non-contact displacement detecting device is increased.
In view of the foregoing, it is an object of the invention to provide a restriction for the movement of the rotational shaft in the axial direction with a low cost construction.
According to the present invention, a non-contact displacement detecting device including a rotational member, a non-rotational member relatively rotatable with the rotational member, a permanent magnet fixed with one of the rotational member and the non-rotational member, a sensor portion fixed with the other rotational member and the non-rotational member and detecting displacement between the rotational member and the non-rotational member. The non-rotational member has a housing and a holder fixed to the housing; the housing supports the rotational member rotatably and restricts one axial direction movement of the rotational member. The holder forms a plurality of contacting points in contact with the rotational member, and restricts the other axial movement of the rotational member.
According to a first aspect of the present invention, as the non-contact displacement detecting device includes a housing for supporting the rotational member rotatably and restricting a movement in one axial direction of the rotational member, and a holder for contacting an end portion of the rotational member at a plurality of contact points for the rotational member and restricting a movement in the other axial direction, the movement of the rotational member in the axial direction is restricted. Further, as the end portion of the rotational member contacts the holder at a plurality of contact points, the movement of the rotational member in the axial direction is regulated, and a friction force between the rotational member and the holder can be reduced. Accordingly, since conventional groove processes for the rotational member and extra parts (e.g., clip, etc.) for restricting the movement of the rotational member are not needed so as to restrict the movement of the rotational member in the axial direction, the device can be made at a low cost.
According to a second aspect of the present invention, the rotational member includes a magnet supporting portion for supporting the permanent magnet, the holder including an opening in which the rotational member is disposed, and a restricting portion for contacting an end portion of the magnet supporting portion on an inner portion of the opening. Thereby, a movement in one axial direction of the rotational member is restricted by the end portion of the housing in the axial direction, a movement in another direction is restricted by the restricting portion formed at the inner portion of the opening of the holder, the movement in the axial direction can be regulated by a simple construction. Further, as the end portion of the magnet supporting portion in the axial direction contacts with the housing, the movement of the rotational member in the axial direction can be restricted, whereby a device having a large number of parts is not needed, and the movement in the axial direction can be restricted with a simple construction.